Recyclable Pd (II) Catalysis on Polymer and Natural Products Supports

Three palladium-complexed compounds were prepared and applied successfully in catalyzing many reactions such as Heck and Wacker reactions and also used in carbonylation of olefin. Polymeric polyimine palladium catalyst 12 was prepared from palladium metal immobilized on a polyimine polymer11. This polymer was prepared by condensation of a dialdehyde (1,4benzenedicarboxaldehyde 10) and diamine (ethylene-diamin). Then Palladium metal was introduced on the polymer to give the catalyst. The prepared polymer catalyst was used in synthesis of 2-hydroxy cycloketones and 2-methoxycycloketones as follows: 2-hydroxy cyclohexanone 15 from cyclohexanone, 2-methoxycyclohexanone 31 from cyclohexanone, and α-hydroxy acetophenone 16 from acetophenone. The products were characterized spectroscopicaly using GC, NMR, IR as well as elemental analysis. The used complex catalyst was reused in the second and third catalytic cycle after washing it with toluene. The reactivity of the catalyst was not diminished in the second and third cycle. However we failed to estimate the percent of Pd remained in the complex after the third usage. In the second part of this work we prepared two complexes from the cheap starting material Curcumin 6. Curcumin, a natural product, along with two other curcuminoids 7 and 8 were extracted from turmeric. The mixture obtained was 3.57g (11.3% yield). The majority of this yield (88%curcumin ) was reduced in the presence of Pd/H2, to THC 24 which then reacted with 2 equivalents of benzylamine to give THCDBI 25 and then palladium was introduced on it. Pd+2 was prepared from oxidation of palladium sponge Pd0 in the presence of acetonitrile, nitrosonium tetrafluoroborate salt and freshly distilled acetonitrile. The reacture mixture was carried out with stirring under N2 to give a yellow golden solid. The yellow solid was filtered, washed with hexane, and dried under vacuum. The produced complex Pd (II)-THCDBI 26, was used to convert cyclopentanone to α-hydroxycyclopentanone 30,cyclohexanone to 2-hydroxycyclohexanone 15, 2-methylcyclohexanone to 2-hydroxy-6-methylcyclohexanone 33 and Propiophenone to 2-hydroxypropiophemone 35. All of the prepared products were characterized spectroscopically using GC, NMR, IR as well as elemental analysis. In the third part, we prepared the last complex which is THCDI-Pd complex 28. THC 24 was reacted with excess ammonia gas to produce light brown solid in 87% yield which turned out to be Tetrahydrocurcuminoids imine (THCDI) 27. Compound 27 was analyzed by 1H and 13C NMR. In the last step of the synthesis, palladium ion Pd+2 was introduced into the curcumin-imine compound (THCDI) to form the complex THCDI-Pd 28. The IR spectral data indicate the presence of Pd in the new complex since the band for C=N dropped by 35 cm-1. This drop is due to the formation of Pd-N bond and as a result of back bonding from 4d orbitals of the metal to the empty *π of the C=N bond, and so the bond order of C=N decreased causing the IR frequency to shift down. The prepared complex Pd (II)- THCDI 28 was used in the synthesis of 2-hydroxycyclohexanone 15, 2-hydroxy,6-methyl-cyclohexanone 33, and 2-hydroxypropiophemone 35. All of the spectroscopic analysis were in agreement with the results; however, we failed to calculate exactly the amount of Pd metal left in the residue for the polymeric complex. On the other hand we prepared and applied successfully the polymeric complex and hence a recyclable and environmentally friendly complex became possible.